Stable reference apparatus



NOV- 28, 1957 J. H. KABAIAN ETAL 3,354,724

STABLE REFERENCE APPARATUS Filed Oct. 2, 1964 INVENTORS United StatesmPatent C) 3,354,724 STABLE REFERENCE APPARATUS Jimmy H. Kabaian, Lynwood', and James F. McGurn, Anaheim, Calif., `assignors to North American Aviation,

Inc.

Filed Oct. 2, 1964, Ser. No. 401,184 s Claims. l(c1. 73s05) This invention relates to an inertially stable reference apparatus and more specifically to means for torquing a string type oscillatory stable reference apparatus.

In United States Patent No. 3,106,847, dated Oct. 15, 1963, to Mullins et'al., there is disclosed a vibratory string type stable referenceapparatus. In copending application, Ser. No. 422,995, entitled Stable Reference Apparatus, -le'd Jan. 4, 1965 in the name of W. H. Quick and assigned to the assignee of the present application there is disclosed a means for torquing the vibratory plane of the vibrating string of the above mentioned patent. The embodiment of the invention disclosed in the present application includes an improved method of torquing such a vibrating string reference apparatus.

An object of the invention is to provide a new and improved torquing means for torquing a vibrating string stable reference apparatus.

Another object of the invention is the provision of a torquing means for providing variable torquing of a vibrating string reference apparatus.

A still further object of the invention is to provide a high speed detector type circuit for accurately controlling the'torquing of a vibrating string reference apparatus.

In order to accomplish the above objects, a unique torquing device is employed which produces a plurality of torqui'ng"signals for torquing a vibratory string reference apparatus in one direction. By so doing, the string can be selectively torqued at a fine or a coarse rate.

Other objects of the invention will become apparent from the following description taken in conjunction with the drawing.

The above mentioned patent and patent application illustrate a vibrating string type reference apparatus describing means for vibrating the string apparatus and -meansfor torquing the vibrating string. In the present invention, the vibrating means for the string is by way of example similar to that described in the above identified patent. The embodiment of the present invention employs such a vibrating means, however, other vibrating mechanism could be used with the torquing of the present invention.

More specifically with reference to the drawing, which illustrates the functional interrelation of the electrical, mechanical and magnetic aspects of a preferred embodiment of the invention, the disclosed vibrating string gyro comprises a ne gold-plated quartz fiber 11 which is stretched to the limit of practicable tension and secured .at two points thereof to a pair of vibratory end bars or diaphragms 12 and 13 which are fixedly secured to each other in the Villustrated mutually spaced relationship by means to be described more particularly hereinafter. The string or fiber 11 is preferably of circular cross-section and may be on the order of one to three mils in diameter, having a lengt-h of one to two inches. The diaphragms 12 and 13, both of which are formed integrally with a quartz supporting body, as described more fully in the above `identified patent, may be of a thickness on the order of 60 mils and are caused to vibrate in opposition so as to move the ends of the string precisely axially, that is, both fdiaphragms move inwardly together and outwardly tog'et'her.l Thevvibratingsys'tem thus formed is dynamically balanced-'so thatQ-the resulting Q is high. A high degree of symmetry of the vibrating diaphragms 12, 13 is employed 3,354,724 vPatented Nov. 28,- 1967 ICC to insure that the motion of the string end points is solely axial. F or purposes of maintaining stability of the reference plane of a device of this nature, it is desirable that the variation in tension of the string during its vibration is held to a minimum. For example, despite all precautions, some transverse vibration of the support will be imparted to the string support points in such a way as to produce an elliptical vibratory string path. With such an elliptical path, a variation in tension of the string due to nonlinearity will give rise to undesired precession, that is, rotation of the plane of vibration. By proper choice of initial tension and the dimensions determining frequency, and by controlling the amplitude of the end motion, the tension variation can be greatly reduced. The amplitude of the end motion is governed by t-he operation of the longitudinal driving system which will be described below, together with the dimensions of the vibratory diaphragms. The thickness and distance between supporting points of such diaphragms will govern the resonant frequency thereof at which they are driven. The frequency of the resonant drive is twice that of the string. The string mass per unit length together with the tension is appropriately adjusted for the desired amplitude length ratio. Such a ratio is the ratio of the amplitude of transverse motion of the string to the length of string between support points. By means of a slight trimming of the driving oscillator amplitude, the minimum tension variation condition will be achieved with the amplitude length ratio very close to the desired value.

` The resonant system comprising the quartz string vi- -brating bars or diaphragms 12 and 13, together with the body which forms the support therefor, may be sealed in a case evacuated to a degree that the Q of' the resonant bars or diaphragms is exceedingly high, on the order of 100,000, and small driving forces are required to maintain oscillation. With the small driving force required, vibration can be imparted to the resonant system by applying an A-C voltage across the capacitor gap to provide an electrostatic drive.

The electrostatic drive comprises a closed loop oscillator including an electrode 14 plated on or otherwise secured to the outer surface of vibratory diaphragm 13 and a capacitive pickoif plate 15 secured to a ease in which the instrument is to be mounted. Pickoff device 14, 15 provides a signal indicating amplitude and phase of the driving motion which is amplified by amplifier 17, the gain of which is controlled by a thermistor 16 in its feedback circuit, and applied to a power amplifier 18. The signal output of the power amplifier 18 is fed to an electrostatic drive comprising the electrode 14 plated on the diaphragm 13 and a second plated electrode 19' fixed to the instrument case. A D-C bias voltage from a source 23 is applied to electrode 14 in order to excite the pickoff and forcing sections, thereby greatly enhancing the efliciency of the A-C voltage in driving the resonator. Thus, it will be seen that there is provided a feedback oscillator including the vibratory diaphragm 13 as a frequency controlling element thereof which applies a driving voltage at twice the string frequency to the diaphragm 13 across the gap between electrodes 14 and 19.

The thermistor 16, having a resistance which decreases with temperature, will operate normally to limit the signal flowing in the driving oscillator circuit, and thus tend to maintain a constant amplitude of vibratiomThis thermistor has a second significant function which arises by reason of the desire for operating the string in the desired constant tension condition. For operation in such a constant tension condition difiiculties are normally encountered in starting vibration when an end drive is employed. For this reason, the thermistor 16 is utilized to cause the starting end motion amplitude to be substantially greater, on the order of approximately percent greater, than the normal operating amplitude. The increased starting arnplitude `is caused by the thermal characteristics of the thermistor 16 which when cold has a relatively high resistance, thereby allowing a larger signal to flow through the driving oscillator circuit. Shortly after the vibration is started and the thermistor heats up, its resistance decreases thereby-decreasing the gain of amplier 17 and the signal ow in the driving oscillator circuit is decreased toa point Where it maintains a steady level.

A torquing current is supplied from the detector circuit to pass through the vibrating string 11. This torquing current cooperates with a magnetic eld passing through the plane of vibration to rotate the plane of vibration. The magneticv assembly 20 Yshown in the drawing, creates this field by way of magnets 21 and 22. Preferably, these magnets are positioned midway between the ends of string 11. Since the action of the current in the string 11 and this magnetic field to produce a torque is described in the above patent and patent application, details thereof will notbe disclosed herein.- In addition, it will be readily understood that the torquing presented in this embodiment could be done by way of inducing a current in the string 11 as shown in the above identiiied patent or by other means suc'h as electrostatically.

An electrostatic pickoff assembly 30 is employed to produce a signal rcurrent that varies as a function of the Velocity of the vibrating string 11. This pickoff assembly includes concave capacitive plates 31 and 32 which are positioned concentric and concave of and with the neutral position of string 11 as illustrated in the drawing. Preferably, these plates are located midway between the ends of string 11. A voltage is maintained between the grounded'string 11 and the plates 31 and 32 by way of a voltage source 35 which is applied to these plates through high rsistances 33 and 34, Thus, paths between plate 31 and the' string 11 and plate 32-and the string 11 are connected te a low impedance AeC differential amplier 36.- The current `into this amplifier varies as the' velocity of the string 11..Tiiat is, when the string 11 approaches plate 31, the` capacitance thereof will increase while the capacitne Between plateV 32 and the string will decrease. Simili'ly 8S the St'rig' 11 approaches' plt 32, the capacitance between thereof will also increase while the capacitance lbetween plate 31. and the string will decrease. This will be renee-:ted as' a variation in the current through the plates 31 and 32.1'1`he signal from plate 31 is applied to the negative input- 36a' of differential amplifier 36. The signal yfrom plate 32 is appliedto the positive input 36b of differential amplifier 36.Tlie current signals at inputs 36a and 36h are a function of the velocity or the stringll and are v1.80 degrees ont of `phase with each other. The diiferentialamplifier 36 is used in order to suppress varialtions in resistor values and supply voltages. Suppression of second harmonie `is also accomplished. Differential amplifier 36 has a stable closed loop gain. The degree of inability of amplifier 36 directly determines the accuracy t' VWhitll a vibrating siting cari be iolqllbd.-

'Ilse output 36e et the amplifier 36 will be a eontinuis Wave which is applied to' an AND gate G3, The output 36d will also be a continuons wave applied to A-ND gate G13. Atfi'e input of amplifier 36, these continuous waves are a function of the' pickoff current from the plates 31 and 32 and are" '180 degrees out of phase with each other. These continuous waves applied to' AND gates G13 and G3 form the basis `for the waveform to be applied to string 11 to rotate its plane of vibration in either a` clockwise or counterl clockwise direction.

TheA output 36C of amplier' 36 is applied through an amplifier: 41 to a zerov crossing detector 42. The signal vapplied ,to the zero crossing detector 42 is an A-C wave. When this A-C Wave goes from a negative value to a positive value, there will be a pulse at the voutput of detector `42, which is applied to AND gate G21. Thus, the .pulses from detector 42 are separated by the time length of 360 degrees of vibration of string 11.

AND gates G1 and G11 determine the direction of rotation that the torquing signal will rotate the plane of vibration. If there is a one on the input of left AND gate G1, the plane of vibration will be rotated to the left. If there is a one on the input of right AND gate G11, the plane of vibration will be rotated in the opposite direction, to the right. The last command from the computer to these gates will determine `the direction of torquing. Preferably some means should be employed to prevent ones simultaneously occurring on both the left and the right gates G1 and G11. 1 1

If there is a one input from the computer on G1, an RS flip-dop F1 will have a true output having a one at its upper output which is applied to gate G2; If there is a one input ongate G11, a one will be applied to the reset input of F1 and the ipdlop F1 will be false with a one on the lower output of F1; This one would be applied to AND gate G12. The AND gates G2 and G12 and flip-flop F3 determine the time width of the torquing signal and the repetition rate of 'the' torquing signal that is, the torquing rate. The RS flip-flop' F2 must receive a command from the computer in order for the torquing signal to be applied to the string 11.` Normally lfrom an initial condition, the RS flip-ilops F2 and F3 are false having a zero at the upper output and a one on the lower output. When a one command is applied to the set iriput of F2, the output of F2 becomes true so that AND gate G21 will pass the next pulse from detector 42 which is representative of the negative to positive going signal from output terminal 36C. When this pulse proceeds through AND gate G21, it renders RS flip-flop F5: true. The AND gate G1 is connected to the complementary input of RS dipop F3; When there is a one on the complementary input of F3, flipdlop F5 will switch states regardless ,of the preceding state. When flip-flop F3 goes true, ,it will apply a one to the AND gates G2 and G12 over line F5. Dependent upon whether a left or right signal has been applied to AND gates G1 or G11, one of 'the AND gates G2 or G12- will be turned on. On the next successive pulse from detector 42, the dip-flop F2 goes false.

The lower output F3" produces a pulse when fiipilop F3 goes from true to false. This pulse renders ilipeop F2 false. This is an indication that one complete torque pulse has been applied to the string 11 and the ip-op F2 is ready to accept the next torque command.

The one so produced at the output of either gate' G2 or G11l will open either AND gate G2 or AND gate G11; rea spectively. If AND gate G15` is opened, its output will be applied to both AND gates G11 and G15. Likewise, if AND gate G3 is opened, its output will be applied to AND gates G1 and G5. The AND gates G5 and G15 have .a relatively high gain whereas AND gates G4 and G11 have a relatively low gain. If a one is present on the coarse input terminal 43, either the output of AND gate G13 will be passed through AND gate G15 or the output of AND gate G3 will be passed through AND gate G5. Likewise ifa one is present on the line input terminal 44, either the torquing signal from G15` will be passed through gate G11 or the torquing signal from gatev G3 will be passed through the AND gate G1. The outputs of the AND gates G4, G5, G14 and G15 are connected through an OR gate G20 to' the vibrating string 11 so as to torque the plane of vibration of the string 11. Hence, it may be said that the torquing of G4 and G11 varies as a function of a constant K1 with the torquing of G5 and G15 varying as a function'v of a larger constant K2.

Hence, it is seen that if it is desired, for example, to pass a relatively large torquing signal to torque the plane of vibration to the left, a one is applied to the input of left gate G1 and a one is applied to the coarse terminal 43. If it is desired to pass a line or a relatively small torquing Vsignal to the left, a one occurs on G1 and also the fine; ter-v minal 44. If a line or coarse signal is desired to rotate the plane to the right, a one is applied at the input of right gate G11 and depending uponv line or coarse output, ones are applied to 43 and/or 44. Thus, it is seen that either fine, coarse, or fine and coarse left torquing can be achieved. The same is true of a right direction torquing. Thus, the string can be torqued the desired amount quickly and accurately.

By the circuitry illustrated, the torquing signals passed through gates G3 and G13 and consequently through the string 11 can only be discrete signals that' have a time width of 360 degrees of Vibration of the spring 11. The reason for this is that the pulse from G21 complements flip-flop F3. The first pulse from G21 sets F3 to true. The second such pulse will always switch the flip-flop F3 from true to false. As the result, the upper output F3 will become zero, closing AND gates G2 and G12 and also as a result, effect closing of AND gates G3 and G13. Thus, it is seen that a complete cycle and only a complete cycle starting at a zero crossing can be passed at one time. A failure circuit, employing a single shot or monostable multivibrator F4 and an AND gate G22, is included. The single shot F1 provides a 11/2 torque period delayed signal triggered by signal on F3". The delayed F3 signal is compared with the output F3 at gate G22. If the output of F3 is still true when the delayed F3" arrives at gate G22, an alarm signal resets E3 to zero thereby inhibiting continuous unintentional torquing due to a malfunction.

It will be understood that such a torquing signal R which would be 180 degrees out of phase with the torquing pulse L is available at the output of gate G13. Pulse R is in phase with the Velocity of the string Whereas pulse L is 180 degrees out of phase with the velocity. This phase relationship enables torquing of the plane of vibration of the string in opposite directions due to the opposite torquing effective between the magnetic field and the current through the string.

Although the invention has been described and illustrated in detail, it is to be clearly understood that this is by way of illustration and example only with the spirit and scope of the invention being limited only by the terms of the appended claims.

We claim:

1. A spatial direction indicator comprising support means, a string mounted between two points of said support means, means for effecting vibration of said string at a predetermined frequency in a vibratory plane, magnetic means providing a magnetic field around said plane of vibration, means for providing a rst alternating current signal having an amplitude which varies in accordance with the vibrations of said string times a factor K1, means for providing a second alternating current signal having an amplitude which varies in accordance with the vibrations of said string times a factor K2 wherein K1 and K2 are not equal, and means for selectively conducting said first or said second signal through said string to effect rotation of said vibratory plane.

2. A spatial direction indicator comprising support means, a string mounted between two points of said support means, means for effecting vibration of said string at a predetermined frequency in a vibratory plane, magnetic means providing a magnetic field around said plane of vibration, means for providing a first alternating current signal having an amplitude which varies in accordance with the vibrations of said string times a constant K1, means for providing a second alternating current signal having an amplitude which varies in accordance with the vibrations of said string times a constant K2 where K2 is smaller than K1, and wherein said first and said second signal have the same time width and phase and means coupling said rst and said second signals to saidstring to effect rotation of said vibratory plane.

3. A spatial direction indicator comprising support means, a string mounted between two points of said support means, means for effecting vibration of said string at a predetermined frequency in a vibratory plane, magnetic means providing a magnetic field around said plane of vibration, means for providing a first alternating current signal having an amplitude which varies as a function of the vibrations of said string times a factor K1, means for providing a second alternating current signal having an amplitude which varies as a function of the vibrations of said string times a factor K2 wherein K1 is less than K1 and wherein said first signal and said second signal are of the same phase, means for providing a third alternating current signal having an amplitude which varies as a function of the vibrations of said string times the factor K1, means for providing a fourth alternating current signal having an amplitude which varies as a function of the vibrations of said during the factor K2 wherein said third and said fourth signals have the same phase, and wherein said third and said fourth signals are opposite in phase to said first and said second signals, and means selectively coupling said first, said second, said third, or said fourth signals to said string so as to selectively effect coarse or fine rotation of said vibratory plane in a first' direction by said first or said second signal respectively and in a second direction by said third or said fourth signal respectively.

4. A spatial direction indicator as set forth in claim 3 wherein said first and said second signals are in phase with the velocity of said string and wherein said third and said fourth signals are degrees out of phase with the velocity of said string.

5. A spatial direction indicator as set forth in claim 4 wherein the time width of said first, second, third and fourth signals is 360 degrees of vibration of said string.

References Cited UNiTED STATES PATENTS 3,047,766 7/1962 Glass. 3,106,847 10/1963 Mullins et al.

JAMES J. GILL, Primary Examiner.

R. C. QUEISSER, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. 3,354,724 November 28, 1967 Jimmy H. Kabaan et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 3l, for "during" read string times Signed and sealed this 21st day of January 1969.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

1. A SPATIAL DIRECTION INDICATOR COMPRISING SUPPORT MEANS, S STRING MOUNTED BETWEEN TWO POINTS OF SAID SUPPORT MEANS, MEANS FOR EFFECTING VIBRATION OF SAID STRING AT A PREDETERMINED FREQUENCY IN A VIBRATORY PLANE, MAGNETIC MEANS PROVIDING A MAGNETIC FIELD AROUND SAID PLANE OF VIBRATION, MEANS FOR PROVIDING A FIRST ALTERNATING CURRENT SIGNAL HAVING A AMPLITUDE WHICH VARIES IN ACCORDANCE WITH THE VIBRATION OF SAID STRING TIMES A FACTOR K1, MEANS FOR PROVIDING A SECOND ALTERNATING CURRENT SIGNAL HAVING AN AMPLITUDE WHICH VARIES IN ACCORDANCE WITH THE VIBRATIONS OF SAID STRING TIMES A FACTOR K2 WHEREIN K1 AND K2 ARE NOT EQUAL, AND MEANS FOR SELECTIVELY CONDUCTING SAID FIRST OR SAID SECOND SIGNAL THROUGH SAID STRING TO EFFECT ROTATION OF SAID VIBRATORY PLANE. 